1. Field of the Invention
Aspects of the present invention relate to an image forming apparatus, and more particularly, to an image forming apparatus including a discharging roller decelerating unit, which allows documents to be uniformly stacked outside of a print unit after printing is complete, and a method of decelerating discharging rollers.
2. Description of the Related Art
An image forming apparatus, such as a printer or a copier, discharges a document on which a print has been performed using discharging rollers and stacks the document in a discharge tray. When the operating speed of the image forming apparatus increases, a document is discharged at a faster rate. In a high-speed image forming apparatus, documents are discharged to the discharge tray at a high speed, and this high speed frequently results in documents being non-uniformly stacked in the discharge tray.
It is preferred that the sheets of printed documents which are discharged at a high speed are uniformly stacked in the discharge tray. There are various methods for solving the above problem. For example, there is a method of reducing the rotation speed of the discharging rollers just before the document is discharged to the outside of a print unit. A decelerating moment of the discharging rollers is determined by a sensor that senses a trailing edge of the document. U.S. Pat. No. 4,693,431 discloses a device for controlling a discharging speed, which includes a paper detecting sensor and discharging rollers.
The document S curls up during printing, due to the document S experiencing the high pressure and temperature of fixing rollers. If the amount of curling in the trailing edges of the documents varies from one document to another, the trailing edge of different documents may pass by a sensing reference point of the sensor at different times, even if the documents have the same size. Consequently, the discharging roller decelerating moments should vary depending on how much curling of the documents takes place, in order to discharge every document uniformly. Otherwise, when the trailing edges of the documents curl up differently according to whether double-sided printing or single-sided printing is performed, the documents may not be uniformly stacked in the discharge tray.